The disclosed invention relates in general to ink-jet devices and more particularly to a structure and method for improving print quality by use of non-emitting orifices. There are a variety of ink jet printers and plotters which produce drops by various means including continuous-jet emitters, in which droplets are generated continuously at a constant rate under constant ink pressure, electrostatic emitters, and drop-on-demand emitters (i.e. impulse jets). These emitters include means for producing a droplet, a nozzle to form the droplet, means for replacing the ejected ink and a power source to energize ejection of the droplet. The nozzles are used to control the shape, volume, and/or velocity of ejected droplets. Such devices typically employ either a single nozzle or a plurality of nozzles formed in a nozzle plate and arranged in a linear or a planar pattern. In impulse jets, pressure pulses are controllably produced in the ink in the vicinity of an emitter to eject one or more droplets of ink through the emitter nozzle. In one type of impulse jet, piezoelectric transducers are utilized to produce the pressure pulses. In another type of impulse jet, electric heaters are utilized to vaporize small regions of the ink to produce the pressure pulses.
In an impulse jet device, it is generally difficult to obtain the combination of pressure pulse, fluid properties, nozzle geometry and refill dynamics which produce a single drop with high velocity and good directional control. In thermal (vapor bubble) ink jet devices and in piezoelectric tranducer ink-jet devices, it is difficult to control the time-history of the pressure pulse. This can compromise the quality of ejected drops because reflow of fluid back into the nozzle due to vapor bubble collapse or piezoelectric transducer relaxation can occur at such time that drop breakoff is adversely affected, such as by producing undesired satellite droplets and/or by deflecting the ejected droplet.
In multi-emitter devices, each emitter is usually connected to a common ink supply plenum. When a pressure pulse is produced in the ink in one emitter, the pressure pulse will be transmitted via the common ink plenum to nearby emitters. Such pressure pulse transmission results in fluidic crosstalk between emitters. This crosstalk can affect the quality of ejected drops through uncontrolled reinforcement or partial cancellation of pressure pulses. In severe cases, a droplet can be ejected out of a nozzle by activating one of its neighbors.
To reduce fluidic crosstalk, existing impulse jet devices typically include a barrier between adjacent emitters to prevent direct transmission of a pressure pulse from one emitter to another. To enable each emitter to refill with ink after ejection of one or more droplets of ink, each emitter is connected to the common ink plenum by a refill channel through the barrier. The amount of crosstalk transmitted via these refill channels can be reduced by increasing the impedance (due to viscosity and inertance) of these channels. Unfortunately, an increase in impedance of a refill channel can detrimentally affect drop quality and reduce maximum drop ejection rate by retarding the rate at which an emitter refills after ejection of a droplet. Thus, because in previous designs the crosstalk impedance is primarily determined by the impedance of the refill channel, a tradeoff exists between repetition rate, drop quality and reduction of fluidic crosstalk.
In co-pending U.S. Pat. application Ser. No. 444,108 entitled A SELF-CLEANING INK JET DROP GENERATOR HAVING CROSS TALK REDUCTION FEATURES filed by Ross R. Allen on Nov. 24, 1982, additional crosstalk reduction is achieved by a plurality of non-emitting drain holes in the nozzle plate connecting the common ink plenum to the ambient atmosphere. At the opening of each refill channel to the common ink plenum is located a drain hole, referred to as an isolator, for the purpose of absorbing and dissipating some of the pressure pulses transmitted into or out of its associated refill channel. These isolators thus enable crosstalk reduction without a concomitant increase in refill channel impedance. However, even in this design, the limited refill rate of an emitter through its narrow refill channel can affect drop quality and reduce the maximum rate of droplet ejection. It should be noted that, although the problems discussed here and the preferred embodiment discussed below, are illustrated in terms of a thermal ink jet device, the same discussion applies to piezoelectric transducer jet devices and other impulse jet devices.